WASHINGTON--U.S. environmental regulators released a plan on Thursday for the nation's power plants and refineries to cut greenhouse gas emissions, pressing ahead with the Obama administration's strategy of tackling the pollution in the absence of federal climate legislation.

The Environmental Protection Agency said it would propose so-called performance standards on greenhouse gas emissions on both new and existing plants beginning in July for power plants and for oil refineries by December. The fossil fuel plants emit about 40 percent of U.S. greenhouse gases.

The plan resulted from an agreement with states, including California and New York, and environmental groups that had sued the agency to regulate emissions of gases blamed for warming the planet.

The standards, the specifics of which have not been established, are also the latest stage of President Barack Obama's effort to drive U.S. policy to combat global warming.

The new rules will come on top of regulations starting on January 2 that require the biggest polluters to get permits for emitting greenhouse gases.

"This is about taking a look at what technologies are available that can cost-effectively achieve reductions in greenhouse gases...it's not establishing a tonnage (of emissions) that should be emitted or shouldn't be emitted," said Gina McCarthy, an EPA assistant administrator on air and radiation.

McCarthy said there were no specifics on the proposed rules and that the timeline was not a first move in setting up a cap-and-trade market on emissions.

The performance standards will be finalized in May 2012 for power plants, and November that year for refineries. New and existing plants can choose available technologies to reduce emissions.

Separately, the EPA said it will issue greenhouse gas permits for Texas, which had refused to adopt rules on emissions. The EPA also said it will issue permits in Arizona, Arkansas, Florida, Idaho, Kansas, Oregon, and Wyoming until state or local agencies are ready to do the job themselves.

The performance standards would add jobs to the economy because they would require many of the hundreds of big fossil fuel plants across the country to adopt new technologies to make their plants more efficient, McCarthy said.

The standards may also require utilities to switch to cleaner fuels, such as from coal to natural gas, but McCarthy said it is also too early to estimate how many aging coal plants might be pushed into retirement.

And refiners complained the standards would harm their businesses. "Regulations can't create technology that doesn't exist or change the laws of physics and economics, so the only way to comply with EPA's proposals would be to inflict massive increases in energy costs and massive increases in unemployment on families across our nation," said Charles Drevna, the president of the National Petrochemical and Refiners Association, said in a release.

But environmentalists applauded the move, saying it will help give power plants certainty to invest in cleaner technologies.

"EPA's commitment to address the dangerous, climate-disrupting pollution from power plants through common-sense national standards will provide important environmental protections and will create economic certainty for vibrant new investments," said Fred Krupp, the president of the Environmental Defense Fund, one of the groups that the EPA settled with.